Larval Dispersal Models Research Articles

Larval dispersal model of coral Acropora in the Karimunjawa Waters, Indonesia

Abstract. Indrayanti E, Zainuri M, Sabdono A, Wijayanti DP, Pranowo WS, Siagian HSR. 2019. Larval dispersal model of coral Acropora in the Karimunjawa Waters, Indonesia. Biodiversitas 20: 2068-2075. Identification of connectivity patterns through the larval dispersal dynamics is urgently needed to support the sustainable larval supply. Many studies on the larval coral distribution have been reported. However, no study of coral larval dispersal has been conducted in Karimunjawa. The purpose of this research was to build a model of coral larval dispersal in Karimunjawa waters. Modeling was carried out by using a 2-dimensional hydrodynamic current approach with a particle tracking module. The larval release was conducted during the full moon in the first transition period (April) and the second transition period (October). The larval source was assumed from around Sambangan waters. Modeling validation was done by comparing the model results to the direct of current measurements with Acoustic Doppler Current Profiler (ADCP). The results of larval dispersal model showed that both the transition seasons I and II were similar in the direction of movement towards the west. This result indicated that currents, tides, and winds influenced the larval dispersal process. Also, the model results showed that Sambangan, Tengah, Cilik, Sintok, the west site of Karimun, Menjangan Kecil, and Menjangan Besar Islands were identified as the location of the larval settlement.

Modelling of larval dispersal of Baltic flounder (Platichthys solemdali) revealed drifting depth as a major factor determining opportunities for local retention vs large-scale connectivity

For flatfishes, transportation of larvae to nursery areas is regarded a key mechanism for recruitment, with adaptations in larval behaviour to reach a suitable habitat. Here we model different possibilities of larval drifting of coastal spawning Baltic flounder Platichthys solemdali (recently identified as a species from European flounder P. flesus) to reveal opportunities for local retention vs large-scale dispersal to ensure settling in coastal nursery areas. Drifting depth, duration of drifting and effects of year and time during season were modelled using 1) a high-resolution local dispersal model, and 2) a large-scale connectivity database. The outcome revealed drifting depth as a major factor affecting larval dispersal. Drift at 10–22 m depth involved retention along the coast with the majority of larvae (≥94% or 69–93% according to 1 and 2, respectively) with end points ≤20 km from the coast enabling further successful migration to nursery habitats. Contrary, larval drift close to the surface resulted in advection with end points in the open sea (72–76%), i.e. loss of larvae, but with a small fraction (5–12%) displaying cross-basin connectivity. The results suggest, in agreement with depth distribution of spawning, a larval behaviour promoting drift in the lower part of the water mass, favouring retention close to coastal nursery areas. Obtained dispersal patterns may sustain both local recruitment but also connectivity with other areas, potentially explaining the low genetic diversity between areas for P. solemdali. Low inter-annual variability in dispersal patterns when drifting at 10–22 m depth suggests that larval drift is not a major bottleneck explaining recruitment variability in P. solemdali in the area. The study highlights the differences in life-history strategies of the species pair of flounder in the Baltic Sea; P. flesus spawning in the deep basins with extensive larval dispersal, and coastal spawning P. solemdali with, according to the model outcome, mainly local larval dispersal for sustaining a viable population, i.e. request for different management strategies.

Evidence of local adaptation in a waterfall-climbing Hawaiian goby fish derived from coupled biophysical modeling of larval dispersal and post-settlement selection

BackgroundLocal adaptation of marine and diadromous species is thought to be a product of larval dispersal, settlement mortality, and differential reproductive success, particularly in heterogeneous post-settlement habitats. We evaluated this premise with an oceanographic passive larval dispersal model coupled with individual-based models of post-settlement selection and reproduction to infer conditions that underlie local adaptation in Sicyopterus stimpsoni, an amphidromous Hawaiian goby known for its ability to climb waterfalls.ResultsOur model results demonstrated that larval dispersal is spatio-temporally asymmetric, with more larvae dispersed from the southeast (the Big Island) to northwest (Kaua‘i) along the archipelago, reflecting prevailing conditions such as El Niño/La Niña oscillations. Yet connectivity is nonetheless sufficient to result in homogenous populations across the archipelago. We also found, however, that ontogenetic shifts in habitat can give rise to adaptive morphological divergence when the strength of predation-driven post-settlement selection crosses a critical threshold. Notably, our simulations showed that larval dispersal is not the only factor determining the likelihood of morphological divergence. We found adaptive potential and evolutionary trajectories of S. stimpsoni were greater on islands with stronger environmental gradients and greater variance in larval cohort morphology due to fluctuating immigration.ConclusionsContrary to expectation, these findings indicate that immigration can act in concert with selection to favor local adaptation and divergence in species with marine larval dispersal. Further development of model simulations, parameterized to reflect additional empirical estimates of abiotic and biotic factors, will help advance our understanding of the proximate and ultimate mechanisms driving adaptive evolution, population resilience, and speciation in marine-associated species.

Use of individual early life traits in larval dispersal models: a multispecies approach

Event Abstract Back to Event Use of individual early life traits in larval dispersal models: a multispecies approach Héctor Torrado1, 2, 3*, Baptiste Mourre4, Núria Raventós1, Carlos Carreras2, 3, Joaquín Tintoré4, 5, Marta Pascual2, 3 and Enrique Macpherson1 1 Center for Advanced Studies of Blanes, Superior Council of Scientific Investigations, Spain 2 Department of Genetics, Microbiology and Statistics, Faculty of Biology, University of Barcelona, Spain 3 Institut de Recerca de la Biodiversitat (IRBIO), Spain 4 Coast observation and prediction system of the Balearic Islands (SOCIB), Spain 5 Instituto Mediterráneo de Estudios Avanzados (IMEDEA), Spain Dispersal is a key process shaping species population structure. In demersal marine species, which usually have sedentary adult phases, dispersion relies on drifting larval stages. However, the dynamics and seasonal variability of seawater masses can greatly determine the connectivity pattern of these species along the same geographic gradient. For this reason, detailed information on the release moment of larvae is needed to obtain accurate esteems of connectivity. Thus, the study of individually based early life traits is fundamental to gather information to properly model larval dispersal capabilities drifting with currents. In this study, we performed backtracking Lagrangian particle dispersion simulations, based on individual early life trait data, obtained from otolith reading, for 1413 juveniles of 9 fish species belonging to 3 families (Pomacentridae, Sparidae and Labridae). For each species, individuals were sampled from 4 to 7 localities at the western Mediterranean (Fig 1). These 9 species reproduce in different times covering the four seasons and pelagic their pelagic larval durations range from 7 to 43 days. With these simulations we obtained larval potential origin maps and connectivity matrices for the 9 species studied. The hatching date and the pelagic larval duration show important effects on larval dispersal modelling both at the intraspecific and interspecific levels. These results prove the utility of using individual early life traits data in larval dispersal modelling. Our case study adds a step forward to an accurate description of larval dispersion and recruitment which is key to understand population resilience under different environmental changing scenarios. Fig 1. Map of the sampled species and their sampling locations. Red lines indicate oceanographic barriers. BF: Balearic front, IC: Ibiza channel, AOF: Almeria-Oran front. Figure 1 Keywords: Western Mediterranean Sea, fish larvae, Dispersal, Lagrangian particle model, Early life traits Conference: XX Iberian Symposium on Marine Biology Studies (SIEBM XX) , Braga, Portugal, 9 Sep - 12 Sep, 2019. Presentation Type: Poster Presentation Topic: Oceanography, Modelling and Dynamics of Ecosystems Citation: Torrado H, Mourre B, Raventós N, Carreras C, Tintoré J, Pascual M and Macpherson E (2019). Use of individual early life traits in larval dispersal models: a multispecies approach. Front. Mar. Sci. Conference Abstract: XX Iberian Symposium on Marine Biology Studies (SIEBM XX) . doi: 10.3389/conf.fmars.2019.08.00088 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 14 May 2019; Published Online: 27 Sep 2019. * Correspondence: Mx. Héctor Torrado, Center for Advanced Studies of Blanes, Superior Council of Scientific Investigations, Blanes, Spain, htorrado@ceab.csic.es Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Héctor Torrado Baptiste Mourre Núria Raventós Carlos Carreras Joaquín Tintoré Marta Pascual Enrique Macpherson Google Héctor Torrado Baptiste Mourre Núria Raventós Carlos Carreras Joaquín Tintoré Marta Pascual Enrique Macpherson Google Scholar Héctor Torrado Baptiste Mourre Núria Raventós Carlos Carreras Joaquín Tintoré Marta Pascual Enrique Macpherson PubMed Héctor Torrado Baptiste Mourre Núria Raventós Carlos Carreras Joaquín Tintoré Marta Pascual Enrique Macpherson Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Resolving the early life history of King George whiting (Sillaginodes punctatus: Perciformes) using otolith microstructure and trace element chemistry

Understanding the early life history processes of fish that lead to recruitment is critical for understanding population dynamics. This study explored the early life history of King George whiting (Sillaginodes punctatus) that recruited to an important nursery area in South Australia in 2016 and 2017. The early life history was reconstructed based on the retrospective analysis of otolith microstructure and chemistry for settlement-stage larvae collected fortnightly from July to November. These fish hatched between March and July, but a 3-week period in May led to 52–71% of recruitment. Recruits from successive sampling occasions differed in age, size and growth rate, potentially related to seasonal changes in water temperature and larval food availability. During both years, there were significant changes in otolith elemental chemistry among the groups of recruits that primarily related to changes in Sr:Ca. There are two hypotheses to account for the differences in otolith chemistry: either (1) a single, primary spawning source and within-season environmental change; or (2) multiple spawning sources. Further investigation with oceanographic models of larval dispersal will help differentiate between these. The retrospective analysis of otoliths has improved the understanding of early life history for this important species, with implications for fishery management.

The PERCEBES project: science for the spatial management of the stalked barnacle fishery in the Atlantic Arc

The PERCEBES project: science for the spatial management of the stalked barnacle fishery in the Atlantic Arc

Ontogenetic changes in swimming speed of silver carp, bighead carp, and grass carp larvae: implications for larval dispersal.

Bighead, silver, and grass carps are invasive in the waterways of central North America, and grass carp reproduction in tributaries of the Great Lakes has now been documented. Questions about recruitment potential motivate a need for accurate models of egg and larval dispersal. Quantitative data on swimming behaviors and capabilities during early ontogeny are needed to improve these dispersal models. We measured ontogenetic changes in routine and maximum swimming speeds of bighead, grass, and silver carp larvae. Daily measurements of routine swimming speed were taken for two weeks post-hatch using a still camera and the LARVEL program, a custom image-analysis software. Larval swimming speed was calculated using larval locations in subsequent image frames and time between images. Using an endurance chamber, we determined the maximum swimming speed of larvae (post-gas bladder inflation) for four to eight weeks post-hatch. For all species, larval swimming speeds showed similar trends with respect to ontogeny: increases in maximum speed, and decreases in routine speed. Maximum speeds of bighead and grass carp larvae were similar and generally faster than silver carp larvae. Routine swimming speeds of all larvae were highest before gas bladder inflation, most likely because gas bladder inflation allowed the fish to maintain position without swimming. Downward vertical velocities of pre-gas bladder inflation fish were faster than upward velocities. Among the three species, grass carp larvae had the highest swimming speeds in the pre-gas bladder inflation period, and the lowest speeds in the post-gas bladder inflation period. Knowledge of swimming capability of these species, along with hydraulic characteristics of a river, enables further refinement of models of embryonic and larval drift.

Resilient reefs may exist, but can larval dispersal models find them?

Resilient reefs may exist, but can larval dispersal models find them?

Response to Bode and colleagues: 'Resilient reefs may exist, but can larval dispersal models find them?'

Response to Bode and colleagues: 'Resilient reefs may exist, but can larval dispersal models find them?'

Quantifying estuarine‐scale invertebrate larval connectivity: Methodological and ecological insights

AbstractThe early life history of many marine organisms includes a dispersive planktonic larval phase which allows for the exchange of individuals among subpopulations. Knowledge of the degree of exchange, or connectivity, is critical to understanding the abundance and distribution of marine populations. Here, we applied geochemical tagging to assess estuarine‐scale larval connectivity among subpopulations of the commercially and ecologically important eastern oyster, Crassostrea virginica. To generate an “atlas” of geochemical signatures associated with spawning sites and potential dispersal pathways from spawning sites, we outplanted recently spawned oyster larvae to stationary moorings and surface drifters, respectively. Using the atlases generated from both outplant methods, we predicted natal origin, and thus larval connectivity, for newly settled oysters (spat) during three field trials over two summers (June 2013, June 2014, and August 2014), within three regions (∼ 35 km × 15 km quadrants) of Pamlico Sound, North Carolina, U.S.A. Patterns of larval connectivity varied both between months and annually but were predominately directed south to north following wind patterns. Predicted self‐recruitment was variable, as up to 100% of spat in a given region displayed signatures consistent with natal origin within that same region. Predicted connectivity patterns varied significantly based on atlases generated from outplanting on stationary moorings vs. surface drifters. For example, drifter‐predicted connectivity followed biophysical larval dispersal models more closely than mooring‐predicted connectivity, while mooring‐predicted connectivity displayed a higher diversity in larval sources. Both connectivity models highlight the need for resource management strategies such as reserve networks to incorporate designs that account for inherent variability in dispersal pathways.

Biophysical Simulations Support Schooling Behavior of Fish Larvae Throughout Ontogeny

Schooling is very common in adult and juvenile fish, but has been rarely studied during the larval stage. Recent otolith micro-chemistry studies of coral reef fish have demonstrated that cohorts of larvae can move through similar paths and settle within a few meters one from another. However, little is known about the processes involved in the formation and maintenance of these cohorts. Here we use a biophysical modeling approach to examine whether local hydrodynamics, various individual behaviors, or larval schooling can explain cohesive patterns observed for Neopomacentrus miryae in the Gulf of Aqaba/Eilat (Red Sea), and whether schooling is feasible in terms of initial encounter probability and cohesiveness maintenance. We then examine the consequences of schooling behavior on larval settlement success and connectivity. Our results indicate that: (1) Schooling behavior is necessary for generating cohesive dispersal patterns, (2) Initial larval encounter of newly-hatched larvae is plausible, depending mainly on initial larval densities, and patchiness, And (3) schooling behavior increases the rate of larval settlement while decreasing the percentage of realized connections. Together with mounting evidence of cohesive dispersal, this numerical study demonstrates that larval schooling throughout the pelagic phase is realistic, and has a significant effect on settlement success and connectivity patterns. Future research is needed to understand the mechanisms of fission-fusion dynamics of larval cohorts and their effect on dispersal. Our findings should be considered in future efforts of larval dispersal models, specifically in the context of marine connectivity and the planning of marine protected area networks.

Asymmetric oceanographic processes mediate connectivity and population genetic structure, as revealed by RADseq, in a highly dispersive marine invertebrate (Parastichopus californicus).

Marine populations are typically characterized by weak genetic differentiation due to the potential for long-distance dispersal favouring high levels of gene flow. However, strong directional advection of water masses or retentive hydrodynamic forces can influence the degree of genetic exchange among marine populations. To determine the oceanographic drivers of genetic structure in a highly dispersive marine invertebrate, the giant California sea cucumber (Parastichopus californicus), we first tested for the presence of genetic discontinuities along the coast of North America in the northeastern Pacific Ocean. Then, we tested two hypotheses regarding spatial processes influencing population structure: (i) isolation by distance (IBD: genetic structure is explained by geographic distance) and (ii) isolation by resistance (IBR: genetic structure is driven by ocean circulation). Using RADseq, we genotyped 717 individuals from 24 sampling locations across 2,719 neutral SNPs to assess the degree of population differentiation and integrated estimates of genetic variation with inferred connectivity probabilities from a biophysical model of larval dispersal mediated by ocean currents. We identified two clusters separating north and south regions, as well as significant, albeit weak, substructure within regions (FST =0.002, p=.001). After modelling the asymmetric nature of ocean currents, we demonstrated that local oceanography (IBR) was a better predictor of genetic variation (R2 =.49) than geographic distance (IBD) (R2 =.18), and directional processes played an important role in shaping fine-scale structure. Our study contributes to the growing body of literature identifying significant population structure in marine systems and has important implications for the spatial management of P.californicus and other exploited marine species.

Potential and limits for rapid genetic adaptation to warming in a Great Barrier Reef coral.

Can genetic adaptation in reef-building corals keep pace with the current rate of sea surface warming? Here we combine population genomics, biophysical modeling, and evolutionary simulations to predict future adaptation of the common coral Acropora millepora on the Great Barrier Reef (GBR). Genomics-derived migration rates were high (0.1–1% of immigrants per generation across half the latitudinal range of the GBR) and closely matched the biophysical model of larval dispersal. Both genetic and biophysical models indicated the prevalence of southward migration along the GBR that would facilitate the spread of heat-tolerant alleles to higher latitudes as the climate warms. We developed an individual-based metapopulation model of polygenic adaptation and parameterized it with population sizes and migration rates derived from the genomic analysis. We find that high migration rates do not disrupt local thermal adaptation, and that the resulting standing genetic variation should be sufficient to fuel rapid region-wide adaptation of A. millepora populations to gradual warming over the next 20–50 coral generations (100–250 years). Further adaptation based on novel mutations might also be possible, but this depends on the currently unknown genetic parameters underlying coral thermal tolerance and the rate of warming realized. Despite this capacity for adaptation, our model predicts that coral populations would become increasingly sensitive to random thermal fluctuations such as ENSO cycles or heat waves, which corresponds well with the recent increase in frequency of catastrophic coral bleaching events.

Auto-correlated directional swimming can enhance settlement success and connectivity in fish larvae

Larvae of coastal-marine fishes have been shown repeatedly to swim directionally in the pelagic environment. Yet, biophysical models of larval dispersal typically impose a Simple Random Walk (SRW) algorithm to simulate non-directional movement in the open ocean. Here we investigate the use of a Correlated Random Walk (CRW) algorithm; imposing auto-correlated directional swimming onto simulated larvae within a high-resolution 3D biophysical model of the Gulf of Aqaba, the Red Sea. Our findings demonstrate that implementation of auto-correlated directional swimming can result in an increase of up to ×2.7 in the estimated success rate of larval-settlement, as well as an increase in the extent of connectivity. With accumulating empirical support for the capacity for directional-swimming during the pelagic phase, we propose that CRW should be applied in biophysical models of dispersal by coastal marine fish-larvae.

Temperate marine protected area provides recruitment subsidies to local fisheries

The utility of marine protected areas (MPAs) as a means of protecting exploited species and conserving biodiversity within MPA boundaries is supported by strong empirical evidence. However, the potential contribution of MPAs to fished populations beyond their boundaries is still highly controversial; empirical measures are scarce and modelling studies have produced a range of predictions, including both positive and negative effects. Using a combination of genetic parentage and relatedness analysis, we measured larval subsidies to local fisheries replenishment for Australasian snapper (Chrysophrys auratus: Sparidae) from a small (5.2 km2), well-established, temperate, coastal MPA in northern New Zealand. Adult snapper within the MPA contributed an estimated 10.6% (95% CI: 5.5-18.1%) of newly settled juveniles to surrounding areas (approx. 400 km2), with no decreasing trend in contributions up to 40 km away. Biophysical modelling of larval dispersal matched experimental data, showing larvae produced inside the MPA dispersed over a comparable distance. These results demonstrate that temperate MPAs have the potential to provide recruitment subsidies at magnitudes and spatial scales relevant to fisheries management. The validated biophysical model provides a cost-efficient opportunity to generalize these findings to other locations and climate conditions, and potentially informs the design of MPA networks for enhancing fisheries management.

Modelling the dispersal of riverine fish larvae: from a raster-based analysis of movement patterns within a racetrack flume to a rheoreaction-based correlated random walk (RCRW) model approach

Recruitment of Chondrostoma nasus and similar fish species in rivers is related to spatiotemporal linkages between larval hatching and nursery habitats. Active swimming behaviour contradicts the assumption that passive particle tracing models can serve as a proxy for larval dispersal models. A racetrack flume with an inshore area of near-natural slope was created to observe individual larval trajectories. A new three-step, raster-based analysis was developed to distinguish four types of movement patterns: active upstream, active downstream, active–passive, and passive. Both larval developmental stage-specific and release site-specific occurrences of these movement patterns were experimentally found for nine flow velocity classes (≤0.225 m·s−1). These current-induced movement patterns, and evaluated durations within them, were used to develop a biased and correlated random walk model that includes rheoreaction — a key behavioural response of fish to flow within rivers. The study introduces the concept and application of a rheoreaction-based correlated random walk model, which coupled with a 3D hydrodynamic model, allows prediction of the spatiotemporal effects of various river discharges, morphologies, and restoration scenarios on larval fish dispersal.

Global mismatch between fishing dependency and larval supply from marine reserves

Marine reserves are viewed as flagship tools to protect exploited species and to contribute to the effective management of coastal fisheries. Yet, the extent to which marine reserves are globally interconnected and able to effectively seed areas, where fisheries are most critical for food and livelihood security is largely unknown. Using a hydrodynamic model of larval dispersal, we predict that most marine reserves are not interconnected by currents and that their potential benefits to fishing areas are presently limited, since countries with high dependency on coastal fisheries receive very little larval supply from marine reserves. This global mismatch could be reversed, however, by placing new marine reserves in areas sufficiently remote to minimize social and economic costs but sufficiently connected through sea currents to seed the most exploited fisheries and endangered ecosystems.

Population genomics meet Lagrangian simulations: Oceanographic patterns and long larval duration ensure connectivity among Paracentrotus lividus populations in theAdriatic and Ionian seas.

Connectivity between populations influences both their dynamics and the genetic structuring of species. In this study, we explored connectivity patterns of a marine species with long‐distance dispersal, the edible common sea urchin Paracentrotus lividus, focusing mainly on the Adriatic–Ionian basins (Central Mediterranean). We applied a multidisciplinary approach integrating population genomics, based on 1,122 single nucleotide polymorphisms (SNPs) obtained from 2b‐RAD in 275 samples, with Lagrangian simulations performed with a biophysical model of larval dispersal. We detected genetic homogeneity among eight population samples collected in the focal Adriatic–Ionian area, whereas weak but significant differentiation was found with respect to two samples from the Western Mediterranean (France and Tunisia). This result was not affected by the few putative outlier loci identified in our dataset. Lagrangian simulations found a significant potential for larval exchange among the eight Adriatic–Ionian locations, supporting the hypothesis of connectivity of P. lividus populations in this area. A peculiar pattern emerged from the comparison of our results with those obtained from published P. lividus cytochrome b (cytb) sequences, the latter revealing genetic differentiation in the same geographic area despite a smaller sample size and a lower power to detect differences. The comparison with studies conducted using nuclear markers on other species with similar pelagic larval durations in the same Adriatic–Ionian locations indicates species‐specific differences in genetic connectivity patterns and warns against generalizing single‐species results to the entire community of rocky shore habitats.

The regional structure of spawning phenology and the potential consequences for connectivity of coral assemblages across the Eastern Tropical Pacific

The coral reefs of the Eastern Tropical Pacific (ETP) are some of the most geographically isolated of the world. A key to understanding their long-term persistence and population recovery via dispersal (i.e. population connectivity), is knowing when the corals spawn in the region. To this end, we reviewed and synthesized the literature on the reproductive phenology of corals (month of spawning) and their dispersal-related characteristics to infer the potential impact on the region’s functional connectivity. We classified the region into four thermal regimes based on long-term mean sea surface temperature (SST) data: Tropical Upwelling, Thermally Stable, Equatorial Upwelling, and Seasonal. Each regime’s unique spawning seasonality was then explored by quantifying the linear dependence between the number of observed spawning events and SST. Finally, the potential impact of this unique regional mismatch in spawning was illustrated using a biophysical larval dispersal model. We found spawning occurs throughout the year in the Upwelling and Thermally Stable regimes (showing low or no linear dependence with SST); whereas spawning had a strong seasonal signal in the Equatorial Upwelling and Seasonal regimes, occurring primarily in the warm months. Considering the region’s mismatch in spawning phenologies, and unique dispersal traits, the simulations of coral larval dispersal across the ETP result in infrequently realized connectivity between ecoregions, low local retention and high self-recruitment, that combined with low recruitment densities in the field indicates more vulnerable populations to disturbance than previously appreciated. The strong relationship between spawning phenology and SST in some regimes suggests a greater susceptibility of these coral assemblages to extreme El Niño and La Niña events and future ocean warming.

Habitat availability and depth‐driven population demographics regulate reproductive output of a coral reef fish

AbstractGlobal habitat decline may displace organisms from optimal environments, increasing reliance on ecosystems with lower habitat suitability and availability. For coral reef fishes, potentially marginal mesophotic coral ecosystems (~30–150 m) may be buffered from anthropogenic stressors; however, variation in habitat quality across depths can alter population demographics, reproductive output, and subpopulation size, potentially restricting the ability for peripheral habitats to support declining populations through larval supply. This study incorporated population density, benthic habitat, and depth‐stratified population demographics to assess bicolor damselfish (Stegastes partitus) subpopulation reproductive output from a broad geographic region encompassing the known depth distribution of the species, including coral reefs in the Florida Keys (0–35 m depths) and mesophotic reefs (~60–90 m) at Pulley Ridge (PR) on the west Florida Shelf. Results indicated that densities of bicolor damselfish peaked in mid‐shelf (10–20 m) and deep‐shelf (20–30 m) habitats, and subpopulation sizes and reproductive output peaked at mid‐depths (10–20 m) in the Florida Keys and declined as depth increased. Subpopulation egg production was affected by differences in demographics across depths, including fish size, sex ratios, and a lower probability and frequency of spawning in deeper habitats. Despite low population densities on mesophotic reefs, the expansive reef area at PR resulted in an estimated subpopulation size that comprised ~14% of the population in the study region, and ~9% of the total reproductive output, indicating that peripheral mesophotic reefs may be sources of larvae that can subsidize declining populations. Larval dispersal and population connectivity models used to inform ecosystem management should incorporate spatially explicit demographics across depth distributions and habitat availability that have substantial effects on egg production and larval supply.